This invention relates to the art of abrasively cleaning surfaces and, more particularly, to a method and system for issuing an alarm and/or interrupting the cleaning operation in response to the occurrence of an undesirable condition during the cleaning operation.
The present invention finds particular utility in lead abatement sandblasting operations and, accordingly, will be disclosed and discussed in detail herein and in conjunction therewith. At the same time, however, it will be appreciated that the invention is applicable in general to any system for abrasively cleaning surfaces wherein the material abrasively removed from the surfaces is collected through the use of a vacuum arrangement in the system.
It is of course well known that lead is hazardous to the health of human beings and is especially harmful to children. Moreover, within the last five years researchers have found that lead is actually much more hazardous than previously thought. It is likewise well known that lead was a common component in industrial paint until about ten years ago, and it is estimated that about eighty percent of all existing bridges, tanks and other structures requiring maintenance by periodic painting currently have paint thereon which is lead based. Proper maintenance of these structures requires a complete removal of the existing paint and repainting thereof about every ten years, and the safe removal of the existing paint, at a reasonable cost, is a serious problem. In this respect, for example, EPA regulations state that a maximum release of dust equal to 150 mg/m.sup.3 over a twenty-four hour period is acceptable during paint removal. A maximum release of airborne lead equal to 1.5 mg/m.sup.3 is allowed. Compliance with these regulations is verified through air samples taken downwind of the surface being cleaned, and if the release is in excess of the regulations, unacceptable contamination of air, soil, water and property has taken place. Still further, OSHA regulations state that persons such as personnel operating lead abatement abrasive blasting apparatus are not to be exposed to airborne lead levels in excess of 50 mg/m.sup.3, and air monitors are worn by such personnel to verify that they have or have not been exposed to excessive lead levels. In view of the increasing concern for the harmful effects of lead, these regulations are expected to be made more stringent in the future. Still further, SSPC standards currently require that a containment be built around an area being abrasively cleaned. Such containments are not only very expensive to construct but, in use, material which is released at the surface being cleaned is only contained in a given area determined by the containment and the latter has no capability with respect to controlling release of material including contaminants from the abrasive cleaning apparatus per se.
Currently, the methods for removing existing lead based paint include conventional abrasive blasting with a containment as mentioned above and which includes an air ventilation system and dust collectors. Accordingly, in addition to the cost of construction and the containment limitation mentioned above, such a system is expensive to operate and maintain. Moreover, while containing contaminants and other materials to the work area and thus minimizing the escape thereof to the surrounding environment, the containment defines an area of confinement for the worker in which contaminants hazardous to the worker's health, including lead, are in an undesirably high concentration due to the confinement. Chemical stripping is another method currently used for removing lead based paints, but this method is also very expensive and, additionally, exposes workers to noxious chemicals as well as fumes emanating from chemical deterioration of the paint, whereby extreme care including special clothing and the like is required to protect workers. Other equipment for abrasively removing lead based paints as well as other materials from surfaces includes systems for impacting steel needles against a surface to be cleaned, hand-held rotary devices which abrasively remove paint or other materials by a rotary peening action, and abrasive blasting apparatus by which an abrasive such as sand is impacted against the surface to be cleaned by air under pressure, all of which systems include a vacuum attachment on the hand held component for recovering material removed from the surface as well as the needles and abrasive material in the corresponding systems. With all devices of the latter type, the face of the hand held component must be maintained in flush contact with the surface being cleaned to avoid or minimize the escape of the abrasive material and the material removed from the surface. If properly positioned in this respect, the vacuum serves to recover the material removed from the surface, or the latter material and the abrasive material by which such material is removed from the surface. If the face of the tool is canted relative to the surface being cleaned, or is moved away from the surface, there is a drop in the vacuum pressure which results in the material being removed from the surface or the latter material and the abrasive material not being sucked into the vacuum attachment but, rather, being dispersed into the surrounding work area. This not only releases contaminants into the latter area but, in connection with abrasive blasting, results in a loss of the abrasive material. In connection with the undesirable release of contaminants and/or abrasive material, a major problem is that the contamination of the surrounding environment as a result of such release is not known until the release has occurred and the damage is done.